Effect of Chlorine Salt Content on the Microstructural Development of C-S-H Gels and Ca(OH)2 at Different Curing Temperatures
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Freshwater resources are scarce in coastal areas, and using seawater as mixing water can alleviate the scarcity of freshwater resources. However, the presence of chloride ions in seawater affects the generation of hydration products and the durability of concrete structures. In order to investigate the effect of hydrated calcium silicate (C-S-H) gel and calcium hydroxide (CH) generation in seawater-mixed cement pastes under 50 °C curing, their microscopic morphology was investigated using differential scanning calorimetry analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The relationship between the amount of C-S-H gel and CH production and the amount of chloride ion dosing, fly ash dosing, and the age of curing were investigated. The degree of influence between hydration products and influencing factors was analyzed using the grey correlation analysis. It was shown that 50 °C curing promoted the hydration reaction and generated more hydration products compared with ASTM standard. The content of C-S-H gel and CH increased with chloride dosage. The content of C-S-H gel increased by 13.5% under 50 °C curing compared with the control group at a chloride dosage of 1.3%. Fly ash is rich in active SiOAims: Chlorine demand by Listeria monocytogenes cells and inactivation of L. monocytogenes by chlorine (0·6–1·0 mg l−1) at different temperatures (4, 20 and 30°C) have been investigated in a batch reactor. Methods and Results: Chlorine demand depended on the microbial concentration and was independent on the initial chlorine concentration and temperature. Chlorine decay was modelled by the addition of two first-order decay equations. Inactivation of L. monocytogenes by chlorine depended on the initial microbial concentration, initial chlorine concentration and temperature. A mathematical model based on a biphasic inactivation properly described survival curves of L. monocytogenes and a tertiary model was developed that satisfactorily predicted the inactivation of L. monocytogenes by different concentrations of initial chlorine at different temperatures. Conclusions: Both available chlorine decay and inactivation of L. monocytogenes by chlorine were biphasic and can be modelled by a two-term exponential model. Significance and Impact of the Study: The biphasic nature of survival curves of L. monocytogenes did not reflect the effect of a change of available chlorine concentration during the treatment. The microbial inactivation was caused by successive reactions that occur after the consumption of the chlorine by the bacterial cell components.
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Ultraviolet (UV)/chlorine draws increasing attention for the abatement of recalcitrant organic pollutants. Herein, it was found that TiO2 would significantly promote the degradation of dimethyl phthalate (DMP) in the UV/chlorine system (from 19 to 84%). Hydroxyl radicals (HO•) and chlorine radicals (Cl•) were the dominant reactive species for DMP degradation in the UV/chlorine/TiO2 system. Chlorine decayed much faster in UV/chlorine/TiO2 compared with UV/chlorine, which is possibly because photogenerated electrons (ecb–) and superoxide radicals (O2•–) have high reactivity with chlorine. As a result, the recombination of photogenerated holes (hvb+) and ecb– was inhibited and the accumulation of HO• and Cl• was facilitated. A kinetic model was established to simulate the reaction process, and it was found that the concentrations of HO• and Cl• were several times to dozens of times higher in UV/chlorine/TiO2 than that in UV/chlorine. The contributions of HO• and Cl• to DMP degradation were 70.3 and 29.7% by model simulation, respectively, and were close to the probe experiment result. In the UV/chlorine/TiO2 system, the degradation of DMP did not follow pseudo-first-order kinetics but the degradation of benzoate fitted well with pseudo-first-order kinetics. This phenomenon was elucidated by the structure of the pollutant and TiO2 and further tested by calculating the adsorption energy (Eads)/binding energy (Eb) with density functional theory. Due to faster decay of chlorine, lower amounts of disinfection byproducts formed in UV/chlorine/TiO2 compared with UV/chlorine. Adding TiO2 into the UV/chlorine system can promote the degradation of recalcitrant organic pollutants in an aqueous environment.
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Ultraviolet
Degradation
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Chlorination of wastewater is recently practiced in Korea. While many researchers have studied the kinetics of aqueous chlorine(HOCl) with nitrogeneous compounds and other organic/inorganic contaminants in drinking water, the researches of wastewater chlorination are relatively few. The purpose of this study was to investigate the chlorine decay kinetics and parameters on wastewater chlorination. Chlorine decay rate increased with increasing initial chlorine concentration. The parameters affecting chlorine decay rate were different in each wastewater treatment plant. One of the most important parameters affecting chlorine decay was initial chlorine concentration, and other parameters such as NH₃-N, total coliform, UV_(254) and Fe were also affected. The decay ratio of chlorine was decreased with increasing initial chlorine concentration, and the disinfection efficiency showed good correlation with the decay ratio.
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Chlorine disinfection is a globally used method to ensure the safety of drinking water. However, it has not always been successful against viruses and, therefore, it is important to find new methods to disinfect water. Seventeen different coliphages were isolated from the treated municipal wastewater. These coliphages and MS2 were treated with different dosages of chlorine in drinking water, and a combined chlorine/ultraviolet irradiation treatment for the chlorine-resistant coliphages. Chlorine disinfection with 0.3-0.5 mg/L total chlorine (free Cl-dosage 0.12-0.21 mg/L) for 10 min achieved 2.5-5.7 Log10-reductions for 11 sensitive coliphages. The six most resistant coliphages showed no reduction with these chlorine concentrations. MS2 was intermediate in chlorine resistance, and thus it is not a good indicator for viruses in chlorine disinfection. In the combined treatment total chlorine of 0.05-0.25 mg/L (free Cl-dosage 0.02-0.08 mg/L) and ultraviolet irradiation (14-22 mWs/cm(2)) were more effective than chlorine alone, and 3-5 Log10-reductions were achieved for the chlorine-resistant strains. The chlorination efficiency could be increased by higher dosages and longer contact times, but this could increase the formation of disinfection by-products. Therefore, the combination treatment is a recommended disinfection method.
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Ultraviolet
Portable water purification
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The inactivation effect of E.coli with different combination modes of UV and chlorine was compared.The result shows that the combination of UV and chlorine can improve the inactivation effect.However,different combination modes and different doses of UV and chlorine affect the inactivation effect.Simultaneous disinfection with UV and chlorine has lower effect than sequential disinfection.During disinfection with chlorine followed by UV,addition of high-concentration chlorine with short contact time has better disinfection efficiency.During disinfection with UV followed by chlorine,high chlorine dose has high inactivation rate.When the chlorine concentration is the same and the contact time is different,the difference of inactivation effect is not significant.
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The current study measured the available chlorine concentration in commercial and household chlorine bleaches (referred to here as "disinfectants") in the liquid and spray forms. The available chlorine concentration in commercial liquid disinfectants is regarded as 5%. However, the results indicated that the available chlorine concentration in commercial liquid disinfectants was 4.39-6.53%, thus the available chlorine concentration was lower than 5%. Household liquid disinfectants were purchased at different times. Liquid bleach that was purchased 1 month prior had an available chlorine concentration of 5% or higher, while liquid bleach that was purchased 6 months prior had an available chlorine concentration of less than 5%. Liquid bleach that was purchased more than 6 months prior had an available chlorine concentration of less than 5%. As time passed after the liquid bleach was purchased, the lower its available chlorine concentration. Commercial spray bleach had an available chlorine concentration of 2.02-3.08%.
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The mechanism and efficiency of chlorine removal by calcium in different atmospheres were investigated by means of thermogravimetry.The PVC was used as the chlorine emission source.The results indicated that PVC can be used as the chlorine emission surce.The efficiency of chlorine removal by Ca(OH)\-2 is the best in the three calcium compounds.The mechanism of chlorine removal by Ca(OH)\-2 is the same as by CaO.The chlorine removal mechanism in different atmospheres is individual.CaCl\-2 will be decomposed under high temperature.
Thermogravimetry
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Chlorine content,distribution and accumulation,yield and quality of flue-cured tobacco were influenced remarkably by different amount of chlorine applied.Chlorine content and accumulation increased remarkably as increasing chlorine rate.There was a linear relationship between chlorine rate and chlorine content or accumulation.Chlorine distribution in upper leaves increased evidently as increasing the amount of applied chlorine from 0 kg/hm~2 to 48 kg/hm~2;and distribution in middle and lower leaves increased remarkably as increasing the amount of applied chlorine to 96 kg/hm~2;chlorine distribution in stem and roots had degressive trend as decreasing the amount of applied chlorine.Yield,quality and chemical composition were the best with 24 kg/hm~2 of chlorine applied;no chlorine applied or applied chlorine more than 24 kg/hm~2 had worse effects on yield and quality.
Curing of tobacco
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In this study, the factors that leading to loss of chlorine residual in water distribution systems were investigated. A series of experiments performed on real water samples collected from effluent of water treatment plant before chlorination. The results showed that bulk chlorine decay rate varied significantly with the initial chlorine concentration and the organic content of water.Further, this paper explores the performance and the potential applicability of the parallel first order model and second order model to represent the bulk chlorine reactions. The modelling and simulation study lead to define the bulk chlorine coefficients as a function of initial chlorine concentration (Co) and COD by developing mathematical equations related to these parameters.
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